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38 SMT Magazine • August 2015 FeAture by Alex Chan, Paul Brown and Richard Coyle, alcaTel-lucenT; Lars Bruno, Anne-kathrine knoph, EriCSSon; Thilo Sack, CElESTiCA inC.; David Geiger, David Mendez and Ron kulterman, FlExTroniCS inTErnATionAl; Mulugeta Abtew, Iulia Muntele, SAnMinA CorP; kirk vanDreel, PlExuS CorP. Abstract There have been many publications, in- dustry workshops, and symposia that describe process mitigation techniques for minimizing the occurrence of head-on-pillow (HoP) defects during surface mount assembly. These include inspection effectiveness as covered in Part 1 of this two-paper set. This second paper addresses the root cause of the HoP defect—specifically the link between HoP defects and component warpage. Multiple case studies contributed by the participating companies are presented to support the proposal that the current indus- try warpage standard needs to be revised and to demonstrate that further work is needed by the industry to understand the root cause of this defect better. Based on the data from the case studies, the authors propose revised accep- tance criteria that set the maximum warpage at 0.090 mm (3.5 mil) for BGA of 0.8 mm pitch and above. Introduction Head-on-pillow (HoP), head-in-pillow (HiP), head-and-pillow (HnP); regardless of what you call it, it is a defect that is growing in preva- lence. HoP is particularly problematic because the intimate contact between ball and paste can easily escape current x-ray inspection process- es and, in many instances, adequate electrical continuity exists to pass initial electrical test- ing. Eventual separation of what was never a proper metallurgical bond can lead to late stage manufacturing defects and even early stage field return issues. Significant effort has been invested in the study of HoP. As a result, the defect mechanism and its contributing factors have been sub- stantially described in the literature [1–3] . There is wide recognition that package warpage is a primary factor in the formation of HoP. In fact, Collaboration between OEM and EMS to Combat Head-on-Pillowing Defects, Part 2: WarPagE aCCEPtanCE PrOPOSal

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